Field of the Invention
This invention relates to a system for integrally controlling an automatic transmission and an engine. More particularly it relates to improvements in a system for controlling an automatic transmission and an engine, wherein gear stages are automatically switched in accordance with a preset shift map, and engine torque is changed by a predetermined value during shifting to maintain satisfactory shift characteristics.
Automatic transmissions are known to include gear transmission mechanisms, a plurality of frictionally engaging devices, and hydraulic pressure control devices operated to selectively switch the engagements of the frictionally engaging devices, so that any one of a plurality of gear stages can be achieved in accordance with a preset shift map.
Furthermore, in an automatic transmission for a vehicle, of the type described, various systems are known for integrally controlling an automatic transmission and an engine, wherein, engine torque is changed during shifting to obtain satisfactory shift characteristics and durability of the frictionally engaging devices (For example, Japanese Patent Laid-Open No. 69738/1980). More specifically, the system for integrally controlling the automatic transmission and the engine, of the type described intends to change the amount of torque transmitted from the engine during shifting and control the amount of energy absorbed by various members in the automatic transmission or by the frictionally engaging devices so as to complete a shifting within a short period of time under a low shift shock, whereby a satisfactory shift feeling is given to a driver and durability of the frictionally engaging devices is improved.
However, when the control for changing engine torque cannot be carried out due to trouble in a sensor system or a request from the engine side, durability of the frictionally engaging devices is reduced due to an increase in the amount of energy absorbed by the frictionally engaging devices in the automatic transmission. Moreover, a shifting time duration is prolonged therefore worsening the shift feeling. This is caused by the shift tuning data (oil pressure and the like) in the automatic transmission being set in expectation of a decrease in the engine torque by a predetermined value during the shifting.
More specifically, a timing for changing engine torque, when it is an upshift, is needed immediately after the start of an actual change in rotary speed of a rotary member in the automatic transmission. In order to detect this accurately, it is necessary to detect a change in engine rotary speed, in rotary speed of the rotary member in the automatic transmission, or a rise in oil pressure in a hydraulic pressure control device (Japanese Patent Application Nos. 234466/1984 and 272609/1984, not prior art). If trouble occurs in a sensor system which detects said changes, control timing is retarded, and the shift characteristics deteriorate to a considerable extent, or no engine torque change is performed. As a result, durability of the frictionally engaging devices which are set in expectation of a decrease of engine torque is reduced.
When ignition timing is delayed for changing (decreasing) engine torque and the delay is carried out immediately after the cold start of the engine, misfiring, or in extreme case, engine stalling tend to occur because the ignition timing is set behind an optimal timing. Further, when the engine temperature is low and a fuel feed quantity and an intake air flowrate are decreased to decrease engine torque misfiring might occur.
Furthermore, when ignition timing is delayed for changing (decreasing) engine torque, an increase occurs in so-called after-burn, which is caused by an exhaust valve opened before gaseous mixture completely burn in engine cylinders due to the delay of ignition timing. As a result, such a problem is presented that high temperature gas is exhausted into an exhaust pipe, whereby temperature of an exhaust system (exhaust gas temperature, catalyst temperature, exhaust pipe temperature and the like) rises. Sometimes, depending on the type of shifting, the control increases the engine torque. In this case, increasing the feed fuel quantity or the intake air flowrate, changes (increases) engine torque for example, the temperature of the exhaust system is raised. The rise in the temperature of the exhaust system caused by changes in engine torque during shifting as described above presents no problem, as long the shift frequency is normal.
However, when the shift frequency is high, the temperature of the exhaust system rises to a tolerance value or more, therefore reducing the durability of an exhaust manifold. Further, in an engine system having a turbocharger, there is a possibility of causing an adverse effect on the turbine blades on the exhaust side. If the feed fuel quantity and the intake air flowrate are frequently decreased to reduce engine torque, there is a possibility of causing engine misfire, deterioration of exhaust gas ingredients and the like.
Consequently, the above-described disadvantages are avoided, when the shift frequency is high, by designing routines relating to engine torque control, by setting a map of an engine torque change value and the like.
Furthermore the above-described disadvantages are avoided even when an engine torque control for shifting is performed when the engine temperature is low by designing routines relating to the engine torque control, by setting of a map of an engine torque change value and the like.
However, a lag angle value of ignition timing is set, at a value rather low from the above-described viewpoint for example, a lowered value of engine torque should naturally be obtained, thus presenting such a problem that the proper purpose of control for improving the shift characteristics including durability of the frictionally engaging devices cannot be satisfactorily displayed.
If in the above-described system means for controlling the engine, means for controlling the automatic transmission, and further, means for controlling the engine torque change are formed integrally with one another, then such problems are presented that the capacity of the computer is increased which leads to increased costs, and it is disadvantages to mount it onto a vehicle having many restritions for space capacity. Furthermore, there are cases where the engine torque control is not needed in relation to uphill or downhill grade, in relation to magnitude of engine output, and, in the case of taking into account the properties of wide application, the integral type may be disadvantageous. Now, if these control means are of a distributed type, as the case may be, such as possibilities occur that the number of connections for connecting the means to one another is increased to make wirings complicated, or disadvantages from a failsafe viewpoint are presented.